1. Field of the Invention
The present invention relates to a double-sided semiconductor structure and to a method for manufacture thereof.
2. Discussion of the Related Art
Integrated circuits in CMOS (Complementary Metal Oxide Semiconductor) technology of a conventional type generally comprise devices of a P type and of an N type formed in a coplanar way, on the same level of a semiconductor substrate of a wafer. In addition, in the same substrate, there are frequently formed other devices, such as for example diodes. Some process steps are common to all the devices obtained in said substrate, but many other steps require being performed separately. In this case, appropriate masks are used for protecting some areas of the substrate during processing of other areas of the same substrate. Furthermore, above all in the case of formation of high-performance devices, it is frequently advantageous to use materials and process steps that are different for each device. Obtaining said devices on separate wafers not only increases the production costs, but introduces problems of connection of contacts and delay in propagation of the signals in the case where different devices have to be housed in one and the same package and operate jointly.
A solution for increasing the production density of MOSFET devices has been proposed in the U.S. Pat. No. 7,485,508, which describes a method for forming horizontal-conduction MOSFET devices, electrically insulated from one another, on opposite sides of a substrate of a SOI (Semiconductor-On-Insulator) type. In this case, MOSFET devices of an N type are formed on one side of the SOI substrate and, separately, on the opposite side of the SOI substrate MOSFET devices of a P type are formed. The electrical contacts for all the devices provided in the SOI substrate are obtained on just one side of the SOI substrate itself, by formation of conductive vias. Said solution enables an increase in the density of the devices for a single wafer, but does not solve problems of performance, connection of contacts, and delay in propagation of the signals involved.
An aim of the present invention is consequently to provide a double-sided semiconductor structure and a method for manufacture thereof that will enable the above drawbacks to be overcome.
According to one embodiment of the present invention, there is provided a semiconductor structure comprising a substrate of semiconductor material of a first type of conductivity, a first semiconductor layer arranged in direct electrical contact with the substrate on a first side of the substrate, a second semiconductor layer arranged in direct electrical contact with the substrate on a second side of the substrate, a first active electronic device formed in the first semiconductor layer; and a second active electronic device formed in the second semiconductor layer.
According to another embodiment of the present invention, there is provided a method for manufacturing a semiconductor structure comprising the steps of providing a substrate of semiconductor material of a first type of conductivity and having a first side and a second side, opposite to one another, forming, on the first side of the substrate, a first semiconductor layer, forming, on the second side of the substrate, a second semiconductor layer, forming, in the first semiconductor layer, a first active electronic device; and forming, in the second semiconductor layer, a second active electronic device.